Optical fiber with a color marking

ABSTRACT

In an optical fiber (1) with a coating (8) for the cladding of one or more plastic layers containing the fiber core and a color marking (3) on or in the outer plastic layer, the color marking (3) is covered by a further transparent or translucent layer (4).

BACKGROUND OF THE INVENTION

1. Techincal Field

The present invention concerns an optical fiber with a coating for thecladding made of several plastic layers, which surrounds the fiber core,and a color marking on or in the outer plastic layer.

2. Description of the Prior Art

Fibers of this generic type have been known for some time. For colormarking and thereby keeping the conductors separate during splicing orconnecting, a ring-shaped marking is applied to the outer plasticcoating of the conductor, for example by using infrared radiation whichhardens the curable plastics, but colored plastic dash or line markingsare also used, which are hardened by applying ultraviolet radiation(UV). Since the color-marked fibers require further processing, forexample when they are implanted into electrical or optical cables, orinto protective tubes made of plastic or steel, or to manufacture fiberribbons made with these fibers, the usual color markings of today, forexample with an IR ring-shaped marking, do not always satisfy thepresent requirements, for example with respect to wear resistance.Because of the nonhomogeneous rough fiber surface caused by the knownring-shaped marking, there can always be problems when the fiber isprocessed further; also, an increase in attenuation can often not beavoided when the temperature in the optical transmission path changes.But a simple dash or line marking can have its drawbacks as well since,aside from the increase in technical effort, such color markings areoften difficult to distinguish.

If cables with a higher number of fibers, for example more than 12, areused because of the increasing need for optical transmission paths, theprecise identification of the fibers being used already producesdifficulties because not enough different distinguishable colors areavailable. This applies equally to optical fibers made of glass, e.g.quartz glass, and to the plastic fibers used increasingly today forcertain transmission paths.

SUMMARY OF THE INVENTION

Starting from this state of the art, it is an object of the invention toensure a precise identification of any number of fibers, and beyond thatto ensure that the color markings applied during the manufacturingprocess remain, regardless of subsequent further processing steps. Thetransmission properties of the fibers must not be influenced by thechosen color markings during temperature changes.

This task object is fulfilled according to the invention in that thecolor marking is covered by a further transparent or translucent layer.This ensures for example that a color marking of applied rings is notworn off from the fiber surface, or from the surface of the coatingsurrounding the fibers, during further processing.

Special advantages are obtained by further development of the invention,in that the further layer extends along the entire fiber length. It alsoensures the protection of the color marking against mechanical wear; thesmooth surface protection with comparable outer diameters ensuresfurther processing of the marked fiber without any problems. Thecorresponding selection of materials needed for the further layerprovide it with high strength, which on the other hand means that theoften unavoidable increase in mechanical strains due to furtherprocessing of the fiber does not impair the optical properties of theoptical fiber; to the contrary, an improvement of the transmissioncharacteristics can be seen. In addition, the corresponding selection ofmaterials allows the further layer to be used as an additionalprotection against moisture and solvents, which means that otherapplication areas in optical transmission technology can be reached witha fiber constructed according to the invention. Since each color markingis mechanically protected by the translucent or transparent furtherlayer of the invention immediately after the fiber is produced, i.e.before any further processing of the optical fiber, any colorcombination and/or any marking configurations can also be securelyapplied to the fiber according to the invention, for any desiredapplication purposes.

Since the further layer covering the color marking, which is used forlater identification of each individual fiber, must be made of atransparent or translucent material, it may be useful to use clear resinfor the purpose of the invention.

If the further layer is colored, another particularly advantageousvariation of the invention is to make it with a colored resin forexample. This results in a multitude of further color combinations whenthe invention is used.

Resins that are suitable for the purposes of the invention are forexample those based on polyamide, polyester, polyether, polysulfone orpolyurethane. The resins may be those that can be hardened by means ofinfrared radiation, which have found use in the technology as so-calledIR-resins; however, it is especially advantageous to use resins that canbe hardened by ultraviolet radiation, which are so-called UV-resins thathave a higher viscosity than IR-resins and are therefore particularlysuited to make the further layer uniform, because of the color markingapplied under it and over the coated fiber.

In addition to a secure and permanent color marking, by stabilizing theoptical fiber equipped with the further layer against mechanical forcesacting from the outside, and by simultaneously protecting it alsoagainst moisture, acids and such, the purposes of the invention are alsoserved by selecting the thickness of the further layer from an order ofmagnitude of 1-10 μm, preferably 3-6 μm.

Another significant advantage of a fiber according to the invention canbe found in that practically any desired color and configuration of themarking can be selected for placement underneath the further layer. If,as is usual today, ring-shaped markings, perhaps single or double rings,are applied to the fiber covered by the so-called coating, theapplication of this color marking is placed either directly on the outercoating layer, or on a uniform fiber coloring which covers the coating.This possibility already offers a multitude of variations of the coloredmarking. Thus for example, the ring-shaped marking of a fiber cancontain rings of the same color, which are spaced differently withrespect to each other along the fiber, or the ring-shaped marking of afiber can contain rings of different colors. Another advantageouspossibility is that the ring-shaped marking of a fiber is composed ofrings of the same or different colors, which are uniformly spaced alongthe fiber. Of course, it is also possible and advantageous if thering-shaped marking of a fiber contains a combination of differentspaces and different colors, especially when a large number of fibers inan optical cable must be kept precisely separated.

Particularly if the further layer surrounds the fiber as an end-to-endprotective layer, it is important to choose a thickness for this coloredlayer forming the ring-shaped marking, which is suitable for thepurposes of the invention. The thickness of the colored layer formingthe ring-shaped marking is therefore 0.5-5 μm, preferably 1-3 μm.

As already explained, any configurations of markings are possible on thefiber surface or on the coating forming the surface of the fiber,therefore a dash or line marking can be applied instead of thering-shaped marking, or according to another idea of the invention, itcan be integrated into the outer layer of this coating. In that case, itcould also be advantageous to apply an additional dash or line markingto a fiber that already has a different color, or even apply a differentcombination of colors.

If the color marking is applied to the surface in similar form as thering-shaped marking, or if the color marking is more or less integratedinto the surface located underneath, the further layer of the inventionensures in all cases that the color marking is permanent and can beidentified at any time.

Regarding the material of the color marking itself, an IR-curable resinis used for example, but it is also advantageous to use so-calledUV-curable resins instead of the IR-curable resins for the colormarking.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-3 are perspective views of three different optical fibers withcolor markings made in accordance with the present invention andprovided with cut-away portions to illustrate internal structure.

DETAILED DESCRIPTION OF THE INVENTION

The optical fiber 1 illustrated in FIG. 1, with fiber core and claddingmade of quartz glass e.g., has the so-called coating 2, which iscomposed of one or more plastic coatings to protect the fiber 1. A colormarking in the form of spaced colored rings 3 is placed directly on thiscoating 2, the material of which is an IR- or UV-curable resin. Thethickness of the colored rings in the configuration example is 3-4 μm,which is the distance surface of the colored rings 3 from the surface ofthe coating 2, so that mechanical wear of the colored rings must beanticipated when this fiber is processed further. To prevent this in areliable manner, the invention provides a further transparent ortranslucent layer 4, which covers the entire length of thecolor-identified fiber. The material of this further layer 4 is forexample a UV-curable polyamide- or polyurethane-based resin, which fillsthe area 5 between each two colored rings, as well as providing a coveron the colored rings 3. With the assumed 3 μm thickness of the coloredrings 3, the thickness of the further layer 4 is 5 μm for example, sothat all colored rings 3 are covered and the areas 5 between each twocolored rings 3 are filled by the material of the further layer. Thisachieves a continuous protection of the color marking.

In the illustrated configuration example, the colored rings 3 have thesame distance, but these distances can of course be varied, and thecolor marking in the form of colored rings 3 can also be applied to analready colored fiber.

Further color variations, and thereby further distinguishingpossibilities, are provided if the further layer 4 according to theinvention is colored or dyed, for example if it is made of a coloredresin. For example, black or blue single or double rings 3 made of anIR-curable resin can be covered by a yellow, red, blue or green-dyed,preferably UV-curable resin layer 4, which has a higher viscosity. Thecolored single or double rings 3 can be easily identified, since thefurther colored layer 4 according to the invention is at leasttranslucent. The selection of contrasting color combinations makes themarked fiber more identifiable.

Deviating from FIG. 1, FIG. 2 illustrates a fiber 6 made of glass orplastic, which is covered by a coating 7 that in turn contains the colormarking. This color marking comprises lengthwise running dashes or lines8 of any color, where this marking is either applied directly to thecoating 7 as illustrated, or is applied thereto if a uniform lengthwiseextending color marking, which itself is colored, is applied to thecoating 7. Like the colored rings in FIG. 1, the dash or line markings 8can contrast against the surface of the plastic used for the coating 7,but the dashes or lines 8 can also be integrated into the plasticmaterial. In all instances, the further layer 9, made of a polyester- orpolyether-based resin for example, is provided to protect the colormarking, and for the purpose of precisely distinguishing between themultitude of optical fibers in cables by means of any markingconfigurations. This resin can either be a clear resin or, as alreadyexplained by means of FIG. 1, a translucent colored resin.

FIG. 3 illustrates another embodiment of the invention, wherein theoptical fiber 10, which again can be made of glass or plastic, issurrounded by the so-called coating 11, specifically a "coating" in thecase of glass fibers, to which the color marking is applied directly, orover an intermediate layer which is colored throughout. In theillustrated embodiment, it comprises spaced dashes or lines 12, possiblyof different lengths that are also repeated periodically, which have adefined thickness and thereby extend beyond the coating 11. These brokendashes or lines, possibly at different distances from each other, arecovered by the further layer 13, which covers the entire optical fiberand thereby securely protects the dashes or lines 12 against wear. Toensure a uniform course of the resin used for the further layer duringthe manufacturing process, a UV-curable resin, for example one based onpolysulfone or polyurethane is used, which fills the interstices 14between every two dashes or lines 12, and above all ensures that thecolor marking remains in the applied form, i.e. as a clear marking withsharp edge areas.

Another differentiation of fibers marked in this manner is provided, ifthe further layer 13 is made of a translucent resin, the color of whichcan be distinguished from the colors or color combinations locatedunderneath.

What is claimed is:
 1. An optical fiber comprising:(a) a fiber core; (b)a cladding surrounding the fiber core; (c) a coating made of at leastone plastic layer surrounding the cladding; (d) a color marking joinedwith the coating; and (e) a further layer extending continuously alongthe full length of the fiber and covering the color marking, the furtherlayer is colored and made substantially solely from a material whichpermits transmission of rays of light so the color marking can be seentherethrough.
 2. An optical fiber as claimed in claim 1, wherein thefurther layer also covers the coating.
 3. An optical fiber as claimed inclaim 1, wherein the further layer is transparent.
 4. An optical fiberas claimed in claim 1, wherein the further layer is translucent.
 5. Anoptical fiber as claimed in claim 1, wherein the further layer is madeof a colored resin.
 6. An optical fiber as claimed in claim 1, whereinthe further layer has a thickness in a range of from 1 to 10 μm.
 7. Anoptical fiber as claimed in claim 6, wherein the further layer has athickness in a range of from 3 to 6 μm.
 8. An optical fiber as claimedin claim 1, wherein the further layer is made from a UV-curable resin.9. An optical fiber as claimed in claim 1, wherein the further layer ismade from an IR-curable resin.
 10. An optical fiber as claimed in claim1, wherein the further layer is made from a material chosen from a groupconsisting of polyamide, polyester, polyether, polysulfone andpolyurethane.
 11. An optical fiber as claimed in claim 1, the colormarking is made from an IR-curable resin and the further layer is madefrom a UV-curable resin.
 12. An optical fiber as claimed in claim 1,wherein the color marking is applied as an additional marking to analready colored fiber.
 13. An optical fiber as claimed in claim 1,wherein the color marking has a thickness in a range of from 0.5 to 5μm.
 14. An optical fiber as claimed in claim 13, wherein the colormarking has a thickness in a range of from 1 to 3 μm.
 15. An opticalfiber as claimed in claim 1, wherein the color marking is a ring-shapedmarking.
 16. An optical fiber as claimed in claim 15, wherein thering-shaped marking is a plurality of same color rings, which are spaceddifferently from each other along the length of the fiber.
 17. Anoptical fiber as claimed in claim 15, wherein the ring-shaped marking isa plurality of different color rings.
 18. An optical fiber as claimed inclaim 15, wherein the ring-shaped marking is a plurality of color rings,which are equally spaced along the length of the fiber.
 19. An opticalfiber as claimed in claim 15, wherein the ring-shaped marking is aplurality of different colored rings, which are spaced differently alongthe length of the fiber.
 20. An optical fiber as claimed in claim 1,wherein the color marking is chosen from a group consisting of dash andline markings.
 21. An optical fiber as claimed in claim 1, wherein thecolor marking is integrated into an outermost plastic layer of thecoating.
 22. An optical fiber as claimed in claim 1, wherein the colormarking is made from an IR-curable resin.
 23. An optical fiber asclaimed in claim 1, wherein the color marking is made from a UV-curableresin.
 24. An optical fiber as claimed in claim 1, wherein the fibercore is made of glass.
 25. An optical fiber as claimed in claim 1,wherein the fiber core is made of plastic.